Method and device for compressing a composite radius

ABSTRACT

A bow wave in a composite laminate generated during part consolidation is reduced by transmitting atmospheric pressure loads to a region of the part having low compaction pressure due to bridging of a vacuum bag at an edge of the part.

TECHNICAL FIELD

This disclosure generally relates to methods and equipment forfabricating fiber reinforced resin laminates, and deals moreparticularly with a method and device for compressing a radius in thelaminate.

BACKGROUND

Fiber reinforced resin laminates may be consolidated prior to and/orduring curing in order to eliminate voids and other inconsistencies inthe cured part. Consolidation may be achieved by applying pressure tothe uncured laminate using vacuum bagging and/or autoclaving processes.In some cases, a caul plate is placed between the vacuum bag and certainareas of the laminate such as a radius, in order to assure that theapplied pressure is evenly distributed over these areas. In some partgeometries, regions of low pressure may exist over the part for any of avariety of reasons, such as bridging of the vacuum bag over certainfeatures of the part. These low pressure areas may result in a “bowwave” being generated in the outer plies of the laminate, in which anout-of-plane wave of the plies is forced from regions of high pressureto the regions of the low pressure mentioned above. Bow waves areundesirable because they result in out-of-plane fiber distortions thatmay cause voids in the laminate.

Accordingly, there is a need for a method and a device for reducing bowwaves in fiber reinforced resin laminates during consolidation,particularly those that may occur near the edge of a radius in thelaminate. There is also a need for reducing regions areas of lowpressure on the laminate caused by bridging of a vacuum bag.

SUMMARY

The disclosed method and device reduce bow waves in the laminate pliescaused by bridging of a vacuum bag used to consolidate the laminate. Thedevice is relatively simple in construction, is reusable and easilyinstalled. The device is used to compress a region of low pressure areaon the laminate, such as an edge of a radius, caused by bridging of thebag over the radius edge. The device includes a first caul covering theradius, and a second caul covering the first portion and the radiusedge. The second caul may also overlie a second laminate such thatconsolidation pressure applied to the second laminate is transferredthrough the second caul onto the radius edge. In one embodiment, thefirst and second cauls may be integrated to form a single unit. In otherembodiments, multiple devices may be joined together side-by-side. Thedisclosed embodiments may reduce bow waves in laminates during theconsolidation process, resulting in cured parts which may exhibitreduced voids and inconsistencies, and desired mechanical properties.

According to one disclosed embodiment, a method is provided of reducinga bow wave in a composite laminate part during consolidation. The methodcomprises transmitting atmospheric pressure loads to a region of thepart having a low compaction pressure due to bridging of a vacuum bag atan edge of the part. The region of low pressure may be located at anedge of a radius in the part. Transmitting atmospheric pressure loadsmay include applying the transmitted loads at the radius edge using acaul on the part at the region of low pressure.

According to another embodiment, a method is provided of reducing a bowwave produced in a region of low compaction pressure of a first uncuredcomposite part during consolidation in a vacuum bag with a secondcomposite part. The method comprises placing a caul device over thefirst and second parts covering the low pressure region, and using thecaul to apply atmospheric pressure loads to the low pressure region ofthe first part. The region of low pressure may be along an edge of aradius on the first part. Placing the caul includes placing a first caulover the radius and the radius edge on the first part, and placing asecond caul on the second part overlapping the first caul. Using thecaul to apply pressure includes using the second caul to apply pressureto the first caul in the region of low pressure.

According to a further embodiment, a method is provided of compressing aradius section of a fiber reinforced laminate part during consolidation.The method comprises forming a large radius in the part adjacent theradius section, and applying compaction pressure to the part, includingapplying tension on the fibers in the radius section by compressing thefibers in the large radius. Forming the large radius in the partincludes forming an excess curved flange on the part.

According to still another embodiment, a device is provided for reducinga bow wave at an edge of a composite laminate part during consolidation.The device comprises a caul configured to substantially conform to theshape of and apply compaction pressure to the edge. The edge may belocated along a radius in the part, and the caul includes a firstportion adapted to be placed on and apply pressure to the radius, and asecond portion having an extremity overlying the first portion and theedge of the part. The first and second portions of the caul may beformed integral with each other.

In still another embodiment, apparatus is provided for tensioning fibersin a radius of a fiber reinforced composite laminate part duringconsolidation. The apparatus comprises a mandrel having a large radiusin an excess flange area of the mandrel, wherein the large radius has aradius of curvature greater than that of the radius of the part.

In another embodiment, a device is provided for reducing a bow wavegenerated in a radius of a composite laminate part during consolidation.The device comprises a caul for applying pressure to the radius of thepart. The caul includes a first portion adapted to cover the radius andan edge contiguous to the radius in which a bow wave in the part isgenerated. The caul further includes a second portion overlying thefirst portion and the edge of the part for applying pressure to the edgeof the part through the second portion of the caul.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

FIG. 1 is an illustration of a side view of a composite structureassembly.

FIG. 2 is an illustration of a side view taken in the direction ‘2’ inFIG. 1.

FIG. 3 is an illustration of an enlarged sectional view showing theformation of a bow wave in the upper plies of the spar at the end of thestiffener.

FIG. 4 is an illustration of a sectional view of the composite structureassembly, showing the use of a caul device to reduce the bow wave shownin FIG. 3.

FIG. 5 is an illustration of a sectional view of a first caul formingpart of the caul device shown in FIG. 4.

FIG. 6 is an illustration of an end view of a second caul forming partof the device shown in FIG. 4.

FIG. 7 is an illustration of a perspective view of the second caul.

FIG. 8 is an illustration of a perspective view of one side of thestiffener shown in FIGS. 1-4 having the second caul installed thereon.

FIG. 9 is an illustration of an isometric view of another form of thecaul device being installed on the stiffener.

FIG. 10 is an illustration of a perspective view of one side of anotherembodiment of the caul device.

FIG. 11 is an illustration of an isometric view of the opposite side ofthe caul device shown in FIG. 10.

FIG. 12 is an illustration of the caul device shown in FIGS. 10 and 11installed on a pair of the stiffeners.

FIG. 13 is an illustration of a sectional view of a laminate assemblyshowing an alternate method of reducing bow waves.

FIG. 14 is a simplified flow diagram illustrating a method for reducinga bow wave.

FIG. 15 is an illustration of an alternate method of reducing a bowwave.

FIG. 16 is an illustration of a flow diagram of aircraft production andservice methodology.

FIG. 17 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring first to FIGS. 1 and 2, a composite structure assembly 20comprises a stiffener 21, sometimes also referred to as a first part,and a spar 22 sometimes also referred to herein as a second part. Thestiffener 21 is bonded to a spar 22 by a layer of adhesive 40. Thestiffener 21 may comprise a fiber reinforced resin composite, and in theillustrated example, has an I-shaped cross section formed by upper andlower flanges 24, 26 joined together by a web 28. While an I-shape crosssection is shown in the Figures, the stiffener 21 may have other crosssectional shapes, such without limitation, C, J, Z, L and inverted Ushapes. The spar 22 comprises a fiber reinforced resin laminate having aweb 30 and a flange 32 forming an L-shaped cross section, however othercross section geometries are possible, such as, without limitation, a“C” section. The spar 22 may form, for example and without limitation,part of the airframe of an aerospace vehicle (not shown) such as a wingor a stabilizer (not shown).

The web 30 transitions to the flange 32 through a radius 34 definedbetween tangent points indicated by the broken lines 36 in FIG. 1. Asbest seen in FIG. 2, the lower flange 26 of the stiffener 21 overliesand is bonded to the upper surface 35 of the web 32. FIG. 1 illustratesa mandrel 38 for supporting the spar 22 during consolidation and curingof the spar 22. In the illustrated example, the stiffener 21 is apre-cured part that is bonded to the spar 22, however, in otherembodiments, the stiffener 21 may comprise an uncured composite partthat is co-cured with the spar 22. The shapes of the stiffener 21 andthe spar 22 merely illustrate a wide variety of possible part shapes andgeometries.

Referring now to FIG. 3, after the stiffener 21 and the spar 22 areassembled with a layer of adhesive 40 therebetween, a vacuum bag (notshown in FIG. 3) is sealed over the assembly 20, which may then beplaced in an autoclave (not shown) for consolidation and curing. Theradius 34 has an upper edge 45 that is spaced from the outer end 46 ofthe lower flange of the stiffener 21. When evacuated, the bag may bridgeover the edge 45 of the radius 34. Bridging of the bag over the edge 45may result in a region 49 of low compaction pressure at the edge 45 whenautoclave pressure P is applied during consolidation and curing of thespar 22. The applied compaction pressure P results in deformation of thefibers in the upper plies 42 along the radius 34 which urges them tomove in the direction of the arrow 51 toward the region of low pressure49. The movement of the fiber toward to the low pressure region 49 mayresult in the generation of a bow wave 44 in the upper plies 42 of thespar 22 as the plies 42 are being compressed in the other areas of theradius 34. This bow wave 44 may result wrinkles, voids or otherundesired inconsistencies in the spar 22 following curing.

Referring to FIG. 4, in order to reduce or eliminate the bow wave 44shown in FIG. 3 caused by the region 49 (FIG. 3) of low pressure, adevice 48 is installed over the radius 34 of the spar 22 and the lowerflange 26 of the stiffener 21. The device 48 includes a first, bottomcaul 50 covering the radius 34 of the spar 22, including the upper edge45. The upper extremity 56 of the first caul 50 abuts the outer end 26of the lower flange 26. The device 48 further includes a second, topcaul 52 that rests on the lower flange 26 and overlies the upperextremity 56 of the first caul 50. The second caul 52 overlaps the upperextremity 56 of the first caul 50 by a preselected distance D. As willbe discussed below in more detail, in one embodiment, the first andsecond cauls 50, 52 may be integrated into a single unit, while in otherembodiments they may be separate units. A vacuum bag 44 is sealed overthe assembly 20 and is used to apply compaction pressure to the partsand the caul 48.

As shown in FIG. 5, the first caul 50 includes an inside radius Rsubstantially conforming to the radius 34. The first caul 50 has athickness T at its upper extremity 56 which generally matches thecombined thickness of the lower flange 26 and the layer of adhesive 30.The first caul 50 is tapered in its thickness from its upper extremity56 to its lower extremity 58. The reduced thickness of the lowerextremity 58 resulting from this tapering may reduce mark-off impartedto the spar 22 by the first caul 50 during the compaction process. Inother embodiments, the first caul 50 may not be tapered in itsthickness.

Referring to FIG. 6, the second caul 52 includes a slotted web 52 acovering the web 28 of the stiffener 21, and longitudinally extendingflanges 52 b which overlie the flanges 26 on the stiffener 21.

Referring to FIG. 4 in use, the device 48 is installed either as twoseparate units or as a single unit on the assembly 20, such that thefirst caul 50 overlies the radius 34 and has its upper extremity 56abutting the outer end 26 a of the flange 26. The slotted web 52 a ofthe second caul 52 is sleeved over the sides of the web 28 such that theflanges 54 rest on the flanges 26 of the stiffener 21 and the outer end60 overlies and rests on the upper extremity 56 of the first caul 50.With the device 40 installed as described above, the vacuum bag 44 maybe installed over the assembly 20, and the assembly 20 may be processedin an autoclave where pressure P is applied to the assembled parts. Thefirst caul 50 applies and distributes the autoclave pressure P to theradius 34 including the upper extremity 56 which overlies the upper edge45 of the radius 34. The autoclave pressure P also presses the flanges52 b against the flanges 26 of the stiffener 21 and against the upperextremity 56 of the first caul 50.

Pressure applied to the lower flanges 26 is transferred by the secondcaul 52 to the first caul 50. The tendency of the upper plies 42 (FIG.3) to produce a bow wave 44 at the edge 45 is resisted by the pressureapplied to the upper extremity 56 by the forward end 60 of the secondcaul 52. Thus, the upper plies 32 (FIG. 3) within the radius 34 areconstrained to remain substantially in-plane during the compactionprocess. Integrating the caul portions 50, 52 into a single part unitprovide the device 48 with additional stiffness 48 which may aid inresisting generation of a bow wave 44 (FIG. 4) or similar heaving orwrinkling of the outer plies 42 at the radius edge 45.

FIGS. 7 and 8 illustrate additional details of the second caul 52. Theupstanding web 52 a includes a longitudinally extending slot 62 therein,and the flanges 52 b extend laterally outward from the web 52 a. Theforward end 60 extends beyond the web 52 a and is adapted to overlie theupper extremity 56 on the first caul 50, as shown in FIG. 4. The secondcaul 52 may be fabricated from any suitable materials that possess therequisite strength and stiffness, including but not limited to a fiberreinforced resin composite such as, without limitation, carbon fiberreinforced epoxy resin. During installation of the second caul 52, theslot 62 receives the web 28 of the stiffener 21 is received within theslot 62, and the flanges 52 b rest on the flanges 26 of the stiffener21.

FIG. 9 illustrates another embodiment of the device 48 in which thefirst and second cauls 50, 52 are integrated into a single unit whichmay be manufactured by molding the caul 48 around the end of thestiffener 21.

Attention is now directed to FIGS. 10, 11 and 12 which illustrateanother embodiment of the device 20 in which multiple devices 48 areintegrated into a unitized structure. In the illustrated example, twoone piece cauls 48 are arranged side by side and formed integral with aconnecting portion 66 and outer extensions 68. The first cauls 50 extendsubstantially continuously across the entire length of the device 48. Asshown in FIG. 12, the device 48 may be installed as a single unit overtwo adjacent stiffeners 21, covering the radius 34 on the spar 22 (notshown in FIGS. 10-12). While the embodiment shown in FIGS. 10-12integrates multiple devices 48 for use with multiple stiffeners 21 havean I-shape cross section, the multiple integrated devices 48 may also beadapted for use with stiffeners having other cross sectional shapes,including, without limitation, C, J, Z, L and inverted U shapes.

Attention is now directed to FIG. 13 which illustrates another method ofcompressing a radius 34 in a manner that reduces bow waves generatedduring consolidation of the spar 30. In this example, the spar 30 islaid up over a mandrel 38 having a lateral extension 38 a. The lateralextension 38 a includes a curved tool surface 70 that forms an excessoutwardly turned flange 72 having a large radius 74 which is generallylarger than radius 34. “Excess” refers to the fact that the primarypurpose of the flange 72 is to place the fibers in the radius 34 intension, and that the flange 72 may not have other substantialfunctional purpose. When consolidation pressure P is applied to the spar30, pressure acting on the large radius flange 72 is greater than thatapplied to the radius 34 and creates tension in the fibers in the upperplies 42 (FIG. 3) which is transferred to the fibers in the radius 34.This tension applied to the fibers in the upper plies 42 in the radius34 may reduce or eliminate wrinkling and/or bow waves 44 in the area ofthe radius 34, including the upper edge 45 (FIG. 3). As used herein,“large” radius refers to a radius 74 that is large enough to produce thetension in the upper plies 42 necessary to reduce or eliminate the bowwaves 44.

Attention is now directed to FIG. 14 which illustrates a method ofjoining composite parts in a manner that reduces bow waves in laminatesduring curing. At step 76, first and second parts 21, 22 are assembled.Next at step 78, a first portion 50 of a caul 48 is placed on the radius34 of the first part 22 covering an edge 45 of the radius 34 andabutting the first part 21. At step 80, a second portion 52 of the caul48 is installed on the second part 21, at least partially overlappingthe first caul 50 at the radius edge 45. In those embodiments where thecaul portions 50, 52 are integrated into a single unit, then steps 78and 80 are combined into a single operation. At step 82, the assembledparts 21, 22 having the caul portions 50, 52 installed thereon arevacuum bagged. At 84, a vacuum is drawn and consolidation pressure isapplied to the bag, using for example, autoclave processing. At step 86,caul portions 50, 52 are used to apply pressure to the radius 34including the radius edge 45 in order to transfer atmospheric pressureloads to the radius edge 45 and reduce the formation of bow waves in thefirst part.

FIG. 15 illustrates the steps of a method of reducing bow waves in alaminate using the apparatus shown in FIG. 14. At step 88, a largeradius 74 is formed in a laminate part 21 adjacent a smaller radiussection 34 in the part 21. At step 80, compaction pressure is applied tothe part 21, including applying tension on the fibers in the radiussection 34 by compressing the fibers in the large radius 74.

Referring next to FIGS. 16 and 17, embodiments of the disclosure may beused in the context of an aircraft manufacturing and service method 98as shown in FIG. 16 and an aircraft 100 as shown in FIG. 17. Duringpre-production, exemplary method 92 may include specification and design102 of the aircraft 100 and material procurement 104. During production,component and subassembly manufacturing 106 and system integration 108of the aircraft 100 takes place. During step 106, the disclosed methodand apparatus may be employed to fabricate composite parts such asfuselage sections which are then assembled at step 108. Thereafter, theaircraft 100 may go through certification and delivery 110 in order tobe placed in service 112. While in service by a customer, the aircraft100 may be scheduled for routine maintenance and service 114 (which mayalso include modification, reconfiguration, refurbishment, and so on).

Each of the processes of method 98 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof vendors, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 17, the aircraft 100 produced by exemplary method 98may include an airframe 116 with a plurality of systems 118 and aninterior 120. The disclosed method and apparatus may be employed tofabricate fuselage sections which form part of the airframe 110.Examples of high-level systems 118 include one or more of a propulsionsystem 122, an electrical system 124, a hydraulic system 126 and anenvironmental system 128. Any number of other systems may be included.Although an aerospace example is shown, the principles of the inventionmay be applied to other industries, such as the automotive industry.

The apparatus embodied herein may be employed during any one or more ofthe stages of the production and service method 98. For example,components or subassemblies corresponding to production process 106 maybe fabricated or manufactured in a manner similar to components orsubassemblies produced while the aircraft 100 is in service. Also, oneor more apparatus embodiments may be utilized during the productionstages 106 and 108, for example, by substantially expediting assembly ofor reducing the cost of an aircraft 100. Similarly, one or moreapparatus embodiments may be utilized while the aircraft 100 is inservice, for example and without limitation, to maintenance and service114.

Although the embodiments of this disclosure have been described withrespect to certain exemplary embodiments, it is to be understood thatthe specific embodiments are for purposes of illustration and notlimitation, as other variations will occur to those of skill in the art.

1. A method of reducing a bow wave in a composite laminate part duringconsolidation, comprising: transmitting atmospheric pressure loads to aregion of the part having low compaction pressure due to bridging of avacuum bag at an edge of the part.
 2. The method of claim 1, wherein theregion of low pressure is located at an edge of a radius in the part,and transmitting atmospheric pressure loads includes applying thetransmitted pressure loads at the edge of the radius.
 3. The method ofclaim 1, wherein transmitting atmospheric pressure loads includesplacing a caul on the part at the region of low compaction pressure. 4.A method of reducing a bow wave produced in a region of low compactionpressure of a first uncured composite part during consolidation in avacuum bag with a second composite part, comprising: placing a cauldevice over the first and second parts covering the low pressure region;and using the caul device to apply atmospheric pressure loads to the lowpressure region of the first part.
 5. The method of claim 4, wherein thelow pressure region is along an edge of a radius on the first part, andplacing the caul device includes: placing a first caul over the radiusand the edge of the radius on the first part, and placing a second caulon the second part overlapping the first caul.
 6. The method of claim 4,wherein using the caul device to apply atmospheric pressure loadsincludes using the second caul to apply pressure to the first caul inthe low pressure region.
 7. A method of compressing a radius section ofa fiber reinforced laminate part during consolidation, comprising:forming a large radius in the part adjacent the radius section; andapplying compaction pressure to the part, including applying tension onthe fibers in the radius section by compressing the fibers in the largeradius.
 8. The method of claim 7, wherein forming the large radius inthe part includes forming an excess curved flange on the part.
 9. Themethod of claim 7, wherein applying the compaction pressure includes:placing a vacuum bag over the part, placing the vacuum bagged part in anautoclave, drawing a vacuum in the bag, and applying pressure to the bagusing the autoclave.
 10. A device for reducing a bow wave at an edge ofa radius on a composite laminate part during consolidation, comprising:a caul configured to substantially conform to the shape of the radiusand apply compaction pressure to the part at the edge of the radius. 11.The device of claim 10, wherein the caul includes: a first portionadapted to be placed on, and apply pressure to the radius, and a secondportion having an extremity overlying the first portion and the edge ofthe radius.
 12. The device of claim 11, wherein the first and secondportions of the caul are formed integral with each other.
 13. Apparatusfor tensioning fibers in a radius of a fiber reinforced compositelaminate part during consolidation comprising: a mandrel having a largeradius in an excess flange area of the mandrel.
 14. The apparatus ofclaim 13, wherein the large radius has a radius greater than that of theradius of the part.
 15. A device for reducing a bow wave generated at anedge of a radius of a composite laminate part during consolidation,comprising: a caul for applying pressure to the radius of the part, thecaul including a first portion adapted to cover the radius and theradius edge, and second portion overlying the first portion and theradius edge for applying pressure to the radius edge through the secondportion of the caul.
 16. The device of claim 15, wherein the firstportion of the caul is tapered in thickness around the radius.
 17. Thedevice of claim 15, wherein the second portion of the caul overlies thefirst portion of the caul and the radius edge.
 18. The device of claim15, wherein the first and second portions of the caul are integral witheach other.
 19. A device for reducing a bow wave generated along an edgeof a radius of a composite laminate spar being joined to a stiffenerhaving lower flanges adjacent the radius edge during consolidation,comprising: a first curved caul for applying pressure to the radius edgeand having a thickness that is tapered along its curvature; and a secondcaul formed integral with the first caul, the second having laterallyextending flanges respectively overlying the lower flanges of thestiffener and having an extremity overlying the radius edge fortransmitting consolidation pressure from the flanges of the stiffener tothe radius edge through the first caul, the second caul furtherincluding a web adapted to be sleeved over the stiffener.
 20. A methodof fabricating a composite structure assembly including a laminate sparjoined to a stiffener, comprising: forming and precuring the stiffener;laying up the laminate spar on a mandrel having a radius; assembling theprecured stiffener with the spar, including placing a layer of adhesivebetween a lower flange of the stiffer and a web of the spar; installinga caul device on the assembly, including molding a first portion of thecaul device to an end of the stiffener overlying a lower flange on thestiffener, and molding a second portion of the caul device integral withthe first portion, including molding the second portion to conform to aradius formed in the spar; vacuum bagging the assembly; placing theassembly in an autoclave; and using autoclave pressure to consolidatethe assembly, including using the caul device to transmit pressure fromthe lower flange to an edge of the radius formed in the spar.